Circular surgical staplers are well known in the surgical field for the ease with which the instrument performs a previously difficult anastomotic stapling operation--the hemostatic joining of two pieces of tubular tissue together with a ring of staples. Such an instrument is ideally suited for intestinal or bowel surgery, and an instrument of this type is the Endopath.TM. ILS Endoscopic Curved Intraluminal Stapler manufactured by Ethicon Endo-Surgery, Cincinnati, Ohio. The circular stapling instrument has a distal stapling head that is available in a variety of sizes to match the organ size of the patient.
Circular stapling instruments are best known for their ability to anastomose or attach two pieces of intestinal or bowel tissue together in an end-to-end fashion. In general, staples are known to provide a good degree of hemostasis when applied to tubular tissue such as intestine or bowel. Circular stapling instruments hold a plurality of staples in an annular array of concentric rings within a body of the distal stapling head. A moveable anvil is used to compress or clamp the pieces of intestinal tissue together between the body and the anvil of the stapling head. A firing trigger is operatively coupled to the stapling head and actuation of the trigger ejects the annular array of staples from the body of the stapling head. The ejected staples pierce the clamped tissue and are formed into a ring of "B" shaped staples that securely join the pieces of intestinal tissue together. A circular blade or scalpel of generally cylindrical shape is located within the stapling head and is advanced distally to sever a small ring or "donut" of excess tissue from between the annular array of formed staples. Severing the donut of tissue opens a passageway between the joined pieces of intestinal tissue. The anastomosed tissue is released from the circular instrument by distally advancing the anvil away from the staple holder and drawing the anvil out through the passageway within the annular array of formed staples. Such a device was disclosed by Becht in U.S. Pat. No. 4,207,898 and by Rothfuss in U.S. Pat. No. 4,319,576.
One improvement to the circular stapler that has been well received by surgeons is the inclusion of a breakaway or backup washer within the anvil of the surgical stapler. The breakaway washer is an annular member of semi-rigid material located within the anvil in a location directly opposite to the circular blade. The annular ring has a pair of spaced annular walls joined together at the proximal end by a thin web of material. The thin web of material faces the circular blade and supports tissue as the circular blade is advanced. The advancing circular blade severs the clamped tissue and is slowed by contact with the thin web of the breakaway washer. A cutting edge of the circular blade is substantially parallel to the thin web of the breakaway washer such that the entire cutting edge contacts the thin web of the breakaway washer in a circular ring of contact. Continued application of force partially severs the thin web of material and the remaining thin web material abruptly breaks due to the applied pressure. As the breakaway washer breaks, the load or force required to advance the circular blade drops abruptly. This abrupt force change provides the surgeon with a clear tactile and an audible indication that the instrument has been fired. A circular stapling instrument having a breakaway or backup washer is taught in U.S. Pat. No. 4,289,133, by Rothfuss.
It is important to note that U.S. Pat. No. 4,289,133 discloses a circular blade having an annular cutting edge that is generally parallel to the thin web of the breakaway washer. The parallelism of the cutting edge to the thin web maximizes the contact area of the blade with the thin web and maximizes the input force required to sever the breakaway washer.
Whereas the breakaway washer was indeed a breakthrough device providing the surgeon with an audible and tactile indication that the anastomosis of the tubular organs is complete, the force required to sever or break the breakaway washer amounted to a large portion of the firing force of the instrument. The force required to break the breakaway washer rises to an abrupt peak over a narrow portion of the firing trigger stroke. An alternate embodiment of the circular blade disclosed in U.S. Pat. No. 4,289,133 is a circular blade having an undulating cutting edge. The undulating cutting edges has both peaks and valleys, and the peaks of the cutting edge contact and slices the breakaway washer before the valleys. The undulating cutting edge does not cut the entire thin web simultaneously and this distributes the cutting of the breakaway washer over a larger part of the firing stroke. This reduces the peak cutting forces, and the blade slices rather than penetrates or punches through the thin web.
Whereas the undulating cutting edge does indeed reduce the load or force to break the washer, it is accomplished by spreading the load over a larger portion of the firing stroke. Testing has indicated that an undulating cutting blade gradually slices the breakaway washer and does not provide the tactile and audible feeling that that is preferred by many surgeons.
Thus, an invention that reduces the peak firing force and provides a tactile and audible signal to the surgeon would be more acceptable. Presently, there is no known surgical anastomosis stapling instrument that can provide an improved interaction between the circular blade and the breakaway washer such that the surgeon is provided with both the desired tactile and audible feedback, and a reduction of the force needed to fire the instrument.